This invention relates to electrical connectors and structures for making electrical connections without lockingly engaging the electrical connection. More specifically, it relates to contact mechanisms for making reliable electrical contact with an ultrasonic transducer mounted in the head, or other end (transducer is on threaded end in some applications) of a fastener, such as a screw or bolt.
Ultrasonics have been used for many years for the detection of cracks and other "faults" in metals and other structural members. Of relatively recent development is the use of ultrasonics for the measurement of the stress applied to a fastener member as a function of the elongation of that fastener as it is tightened against the structure to which it fastens.
Early attempts at this ultrasonic measurement of stress loads introduced into fasteners included McFaul et al., U.S. Pat. No. 3,759,090, who measured fastener elongation with a transducer head manually held against the head of a bolt and interfaced with a glycerin coating used as the acoustic coupling medium. A coaxial cable connected from electronic circuitry was connected to a piezoelectric crystal held in a transducer head assembly.
Like McFaul et al., Moore et al., U.S. Pat. No. 4,014,208, used an ultrasonic transducer held against a bolt head of fastener to make ultrasonic readings. Moore et al. also utilized an acoustic coupling medium such as glycerin. Moore et al., however, placed their transducer within the drive socket of a socket wrench in order to take readings. A hard wired connection, presumable a solder or screw terminal connection, connected the Moore et al. transducer head to their electronic circuitry. Twin lead wire was used.
While both McFaul and Moore could each move their respective ultrasonic transducer heads from one fastener to another, and no modification of a fastener or bolt was needed other than to provide for a flat transducer interface surface, their measurement results were often difficult to repeat and difficult to calibrate because of acoustic losses at the bolt-to-transducer glycerin interface. Moreover, measurements were often affected by an individual technician's manual procedures and by factors such as dust which modified the acoustic coupling interface.
It was desirable, therefore, to implant an ultrasonic transducer, which may be a piezoelectric device, directly and permanently onto a bolt or fastener with a reliable acoustic interface to the fastener. The ultrasonic coupling would, therefore, be repeatably predeterminable at manufacture from fastener to fastener. By doing so, only an electrical connection need be made to the ultrasonic transducer.
Dougherty, U.S. Pat. No. 4,127,788, had provided a bolt having a threaded insert and a threaded cap. A piezoelectric crystal with hard wired electrical connections is embedded in a resin block. This block is secured in mechanical pressure contact within the bolt by tightening the threaded insert against the threaded cap. Electrical connections with the wires extending from the bolt must then be made. This lends to excellent static ultrasonic testing, but eliminates the possibility of ultrasonic testing while tightening the fastener as the wire leads get in the way.
Couchman, U.S. Pat. No. 4,294,122, has focused on the problem of testing in the dynamic state. He has provided a fastener or bolt with a piezoelectric device secured permanently within its end. An electrical contact surface is provided to extend flush with the surface of the end adjacent the piezoelectric device and to be electrically isolated therefrom. A first and second hard wired electrode provides electrical connections between the piezoelectric device and the electrical contact surface and the piezoelectric device and the bolt body, respectively.
Electrical contact to the Couchman fastener embedded piezoelectrical device is made through a spring biased terminal pin carried by a tightening tool and in contact with the bolt end contact surface. The tool is grounded as is the drive socket which is in contact with the bolt body.
Couchman represents an improvement over the other art where reading errors due to a lack of reproducibility of a good acoustic interface between the piezoelectric transducer and the bolt body occurred from unit to unit. By placing an individual piezoelectric transducer in the bolt body, the poor acoustic coupling errors introduced by the manually held transducer head using glycerin are eliminated. Moreover, Couchman has solved the twin lead tangling problems which occurred with Dougherty when the bolt was turned with the wires connected.
However, the Couchman structure presents an opportunity for measurement errors caused by poor electrical connections, i.e., electrical coupling. Couchman relies upon a simple solid probe or pin which is spring biased outwardly from his power wrench socket head. A single electrical line, a spring and the terminal pin extend through a bore or other opening in the power wrench and socket head. During static conditions, an adequate electrical connection may be maintained.
However, during dynamic conditions, i.e., during tightening and especially during high speed assembly, the operation of the power wrench and rotation of the socket head can cause erratic electrical contact between the bolt body and the socket head and between the piezoelectric transducer terminal plate and the electric terminal pin. The Couchman probe pin can bend, rock or break, making readings impossible. It can also jump during rotation, making readings erratic. It is desirable to provide a structure where this does not occur or where its occurrence is greatly reduced. Further, as Couchman relies only upon his drive socket and tool body for his return electrical signal line, grease, dirt and foreign matter on the drive socket, and stray electrical signals from the tool body can interfere with the "sense" readings.
Couchman, U.S. Pat. No. 4,295,377, disclosed a specific rotational coupling that allows the pin to rotate with the fastener. However, it is desirable to provide a structure which eliminates the need for a specific rotational coupling mechanism since it is a recognized problem that the rotation of the fastener relative to the electronics presents a problem in providing reliable electrical contact.
An object of the present invention is to provide an improved electrical contact mechanism for electrically connecting ultrasonic transducers, which have been fixedly mounted on a fastener or bolt with electronic apparatus, while the fastener or bolt is being tightened.
A second object of this invention is to provide an improved electrical contact mechanism which eliminates the need for a specific rotational coupling.
A third object of this invention is to provide such an electrical contact mechanism which can be installed axially into hand wrenches and electrically, pneumatically, or hydraulically powered tightening tools, such as electric spindles, impact wrenches, RANs (right angle unit runners) and other devices.
Another object of this invention is to provide such an electrical contact mechanism which can be installed to extend through a tool socket head and which is capable of maintaining good electrical contact with a contact surface on a bolt head while the bolt is tightened with a tool socket head and which provides a secure twin lead electrical connection.
A further object of this invention is to provide protection of the contact mechanism to secure it from damage during assembly operations, while not interfering with normal operation of the tool and to provide a low cost contact pin which can quickly be replaced.